無法實例化活動ComponentInfo {}：java.lang.NullPointerException

Question

你好，我是Android新手，所以你可以幫我解決我的錯誤。 02：31.350：E/AndroidRuntime時 我要開始遊戲，所以這裏是我的logcat數據庫和活動

logcat的

4月8日至6日出現的錯誤（8261）：致命異常：主

4月8日至六日：02：31.35 0：E/AndroidRuntime（8261）：無法實例化活動ComponentInfo {com.example.windowcard/com.example.windowcard.Grade1}：java.lang.NullPointerException 08-06 04：02：31.350 ：E/AndroidRuntime（8261）：at android.content.ContextWrapper.getPackageName（ContextWrapper.java:127） 08-06 04：02：31.350：E/AndroidRuntime（8261）：at com.example.windowcard.dbHelp。（ dbHelp.java:39） 4月8日至6日：02：31.350：E/AndroidRuntime（8261）：在com.example.windowcard.Grade1（Grade1.java:41）

數據庫

package com.example.windowcard; 

import java.io.File; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.OutputStream; 

import android.content.Context; 
import android.database.Cursor; 
import android.database.SQLException; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteException; 
import android.database.sqlite.SQLiteOpenHelper; 
import android.util.Log; 


    public class dbHelp extends SQLiteOpenHelper{ 

//The Android's default system path of your application database. 
private static String TAG = "dbHelp"; 
private static String DB_PATH = ""; 

private static String DB_NAME = "sample"; 

private SQLiteDatabase myDataBase; 

private final Context myContext; 

/** 
* Constructor 
* Takes and keeps a reference of the passed context in order to access to the application assets and resources. 
* @param context 
*/ 
public dbHelp(Context context) { 

    super(context, DB_NAME, null, 1); // 

    DB_PATH = "/data/data/" + context.getPackageName() + "/databases/"; 
    this.myContext = context; 
} 

/** 
* Creates a empty database on the system and rewrites it with your own database. 
* */ 
public void createDataBase() throws IOException{ 

    myContext.deleteDatabase(DB_NAME); 
    boolean dbExist = checkDataBase(); 

    if(!dbExist){ 
     //do nothing - database already exist 
     this.getReadableDatabase(); 
     this.close(); 
     try{ 
      copyDataBase(); 
      Log.e(TAG, "create Database database created"); 
     } 
     catch (IOException e){ 
      throw new Error ("Error Copying Database"); 

     } 

    } 

} 

/** 
* Check if the database already exist to avoid re-copying the file each time you open the application. 
* @return true if it exists, false if it doesn't 
*/ 
private boolean checkDataBase(){ 


    File dbFile = new File (DB_PATH + DB_NAME); 
    Log.v("dbFile", dbFile + " " + dbFile.exists()); 
    return dbFile.exists(); 

/** 
* Copies your database from your local assets-folder to the just created empty database in the 
* system folder, from where it can be accessed and handled. 
* This is done by transfering bytestream. 
* */ 
private void copyDataBase() throws IOException{ 

    //Open your local db as the input stream 
    InputStream myInput = myContext.getAssets().open(DB_NAME); 

    // Path to the just created empty db 
    String outFileName = DB_PATH + DB_NAME; 

    //Open the empty db as the output stream 
    OutputStream myOutput = new FileOutputStream(outFileName); 

    //transfer bytes from the inputfile to the outputfile 
    byte[] buffer = new byte[1024]; 
    int length; 
    while ((length = myInput.read(buffer))>0){ 
     myOutput.write(buffer, 0, length); 
    } 

    //Close the streams 
    myOutput.flush(); 
    myOutput.close(); 
    myInput.close(); 

} 

public boolean openDataBase() throws SQLException{ 

    //Open the database 
    String myPath = DB_PATH + DB_NAME; 
    myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.CREATE_IF_NECESSARY); 
    // myDatabase = 
    SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.NO_LOCALIZED_COLLATORS); 
    return myDataBase != null; 

} 

@Override 
public synchronized void close() { 

    if(myDataBase != null) 
     myDataBase.close(); 

    super.close(); 

} 

@Override 
public void onCreate(SQLiteDatabase db) { 

} 

@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 

} 

// Add your public helper methods to access and get content from the database. 
// You could return cursors by doing "return myDataBase.query(....)" so it'd be easy 
// to you to create adapters for your views. 

public Cursor getAllGrade1(){ 

    this.openDataBase(); 
    String sql = "Select * from gr1"; 
    Cursor c = myDataBase.rawQuery(sql, null); 
    c.moveToFirst(); 
    return c; 
} 
public String getScore(int score){ 
    this.openDataBase(); 
    String sql = "SELECT * FROM gr1 WHERE _id =" + score; 
    Cursor c = myDataBase.rawQuery(sql, null); 
    c.moveToFirst(); 
    return c.getString(c.getColumnIndex("score")); 
} 
public String getMistakes(int Errors){ 
    this.openDataBase(); 
    String sql="SELECT * FROM gr1 WHERE _id=" + Errors; 
    Cursor c = myDataBase.rawQuery(sql, null); 
    c.moveToFirst(); 
    return c.getString(c.getColumnIndex("Errors")); 
} 

    } 

活動

  package com.example.windowcard; 

      import java.util.ArrayList; 
      import java.util.Collections; 
      import android.app.Activity; 
      import android.app.AlertDialog; 
      import android.content.DialogInterface; 
      import android.content.Intent; 
      import android.database.Cursor; 
      import android.media.MediaPlayer; 
      import android.os.Bundle; 
      import android.os.Handler; 
      import android.view.View; 
      import android.view.View.OnClickListener; 
      import android.widget.Button; 
      import android.widget.EditText; 
      import android.widget.TextView; 
      import android.widget.Toast; 

      public class Grade1 extends Activity implements OnClickListener { 
      TextView tvQuestion,tvQuestionId,tvPlayer1,tvScore,tvMissCount; 
      EditText et; 
      Button submit,next,start; 
      Cursor c; 
      MediaPlayer sonic; 
      Handler mHandler = new Handler(); 
      long startTime; 
      TextView timer,timems; 
      long elapsedTime; 
      final int REFRESH_RATE = 100; 
      String hours,minutes,seconds,milliseconds; 
      long secs,mins,hrs,msecs; 
      boolean stopped = false; 
      String s,timers; 
      int score=1; 
      int miss=1; 
      dbHelp dbh = new dbHelp(this); 
      ArrayList<Integer> rdm = new ArrayList<Integer>(); 
      @Override 
      protected void onCreate(Bundle savedInstanceState) { 
       // TODO Auto-generated method stub 
       super.onCreate(savedInstanceState); 
       setContentView(R.layout.grade1); 
       sonic = MediaPlayer.create(Grade1.this,R.raw.sonic); 
       sonic.start(); 
       sonic.setLooping(true); 
       sonic.setVolume(100, 100); 
       initialize(); 

       } 
      public void updateTimer (float time){ 
       secs = (long)(time/1000); 
       mins = (long)((time/1000)/60); 
       hrs = (long)(((time/1000)/60)/60); 


       secs = secs % 60; 
       seconds=String.valueOf(secs); 
       if(secs == 0){ 
        seconds = "00"; 
       } 
       if(secs <10 && secs > 0){ 
        seconds = "0"+seconds; 
       } 



       mins = mins % 60; 
       minutes=String.valueOf(mins); 
       if(mins == 0){ 
        minutes = "00"; 
       } 
       if(mins <10 && mins > 0){ 
        minutes = "0"+minutes; 
       } 


       hours=String.valueOf(hrs); 
       if(hrs == 0){ 
        hours = "00"; 
       } 
       if(hrs <10 && hrs > 0){ 
        hours = "0"+hours; 
       } 


       milliseconds = String.valueOf((long)time); 
       if(milliseconds.length()==2){ 
        milliseconds = "0"+milliseconds; 
       } 
       if(milliseconds.length()<=1){ 
        milliseconds = "00"; 
       } 
       //milliseconds = milliseconds.substring(milliseconds.length(), milliseconds.length()); 

       (timer = (TextView)findViewById(R.id.tvTime)).setText(hours + ":" + minutes + ":" + seconds); 
       //((TextView)findViewById(R.id.tvTimeMs)).setText(":" + milliseconds); 
      } 
      public Runnable startTimer = new Runnable() { 
        public void run() { 
         elapsedTime = System.currentTimeMillis() - startTime; 
         updateTimer(elapsedTime); 
         mHandler.postDelayed(this,REFRESH_RATE); 
        } 
       }; 
       public void startClick (View view){ 
        if(stopped){ 
         startTime = System.currentTimeMillis() - elapsedTime; 
        } 
        else{ 
         startTime = System.currentTimeMillis(); 
        } 
        mHandler.removeCallbacks(startTimer); 
        mHandler.postDelayed(startTimer, 0); 
       } 
        public void stopClick (View view){ 
         mHandler.removeCallbacks(startTimer); 
         stopped = true; 
        } 

        public void resetClick (View view){ 
         stopped = false; 
         ((TextView)findViewById(R.id.tvTime)).setText("00:00:00"); 
         //((TextView)findViewById(R.id.tvTimeMs)).setText(":0"); 
        } 
      private void refresh(){ 

       c = dbh.getAllGrade1(); 
       c.moveToPosition(rdm.get(0)); 
       rdm.remove(0); 
       tvScore.setText(dbh.getScore(score)); 
       tvMissCount.setText(dbh.getMistakes(miss)); 
       tvPlayer1.setText(s); 
       //tvQuestion.setText(c.getString(c.getColumnIndex("Question"))); 
       tvQuestion.setText(c.getString(1)); 
       et.setText(""); 
      } 


      private void initialize() { 
       // TODO Auto-generated method stub 
       submit= (Button) findViewById(R.id.b1); 
       //tvQuestionId = (TextView) findViewById(R.id.tvQuestionId); 
       tvPlayer1 = (TextView) findViewById(R.id.tvPlayer1); 
       tvScore = (TextView) findViewById(R.id.tvScore); 
       tvQuestion = (TextView) findViewById(R.id.tvQuestion); 
       tvMissCount = (TextView) findViewById(R.id.tvMissCount); 
       start = (Button) findViewById(R.id.bStart); 
       et = (EditText) findViewById(R.id.et1); 
       Intent z = getIntent(); 
       s = z.getExtras().getString("PlayerName"); 
       submit.setVisibility(View.INVISIBLE); 
       et.setVisibility(View.INVISIBLE); 
       tvQuestion.setVisibility(View.INVISIBLE); 
       //Bundle receive = getIntent().getExtras(); 
       //hold = receive.getString("PlayerName") 

       for(int count=0; count<10; count++){ 
        rdm.add(count); 
       } 
       Collections.shuffle(rdm); 
       refresh(); 
       final MediaPlayer mp = MediaPlayer.create(this, R.raw.answerright); 
       final MediaPlayer mp2= MediaPlayer.create(this, R.raw.answerwrong); 

       start.setOnClickListener(new View.OnClickListener() { 

        @Override 
        public void onClick(View arg0) { 
         // TODO Auto-generated method stub 
         if (start.isClickable()){ 
          et.setVisibility(View.VISIBLE); 
          submit.setVisibility(View.VISIBLE); 
          tvQuestion.setVisibility(View.VISIBLE); 
          startClick(arg0); 
          start.setVisibility(View.INVISIBLE); 
         } 
        } 
       }); 
       submit.setOnClickListener(new View.OnClickListener() { 

        @Override 
        public void onClick(View v) { 
         // TODO Auto-generated method stub 
         if(et.getText().toString().equalsIgnoreCase("")){ 
          Toast.makeText(getApplicationContext(), "You need to answer first the question before proceeding to the next question", Toast.LENGTH_SHORT).show(); 
         }else{ 
          if (c.getString(c.getColumnIndex("Answer")).equalsIgnoreCase(et.getText().toString())){ 
           mp.start(); 
           if(score==10){ 
            stopClick(v); 
            timers = timer.getText().toString(); 

           // dbh.insertRecord1(s, score,timers,miss); 
            resetClick(v); 
            AlertDialog diaBox = makneAndShowDialogBox(); 
            diaBox.show(); 
            diaBox.setCanceledOnTouchOutside(false); 

            //Toast.makeText(getApplicationContext(), "Congratulations!", Toast.LENGTH_LONG).show(); 
            sonic.release(); 
            //Intent a = new Intent(Grade1.this,Menu.class); 
            //startActivity(a); 
            //finish(); 
           } 
           String Score = tvScore.getText().toString(); 
           score++; 
           //String newScore = dbh.getScore(score); 
           refresh(); 
          } 
          else{ 
          mp2.start(); 
          String Miss = tvMissCount.getText().toString(); 
          miss++; 
         // String newMiss = dbh.getMistakes(miss); 
          refresh(); 
          } 
         } 




       } 
       }); 
      } 
       private AlertDialog makneAndShowDialogBox() { 
        // TODO Auto-generated method stub 
        AlertDialog myDialogBox = new AlertDialog.Builder(this) 
        .setTitle("Congratulations!!") 
        .setMessage("Congratulations on finishing the game!") 
        .setPositiveButton("Main Menu", new DialogInterface.OnClickListener() { 
         public void onClick(DialogInterface dialog, int whichButton) { 
          Intent i = new Intent(Grade1.this,Menu.class); 
          startActivity(i); 
          finish(); 
          dialog.dismiss(); 
         } 

       }) 

       .create(); 
       return myDialogBox; 






      /** next.setOnClickListener(new View.OnClickListener() { 

        @Override 
        public void onClick(View v) { 
         int count = 0; 
         // TODO Auto-generated method stub 
         if(count==40){ 
          Intent a = new Intent(Grade1.this,Menu.class); 
          startActivity(a); 
          finish(); 
         } 
         count++; 
        refreshgame(); 
        } 
       }); 

      **/ 


         } 

         @Override 
         protected void onPause() { 
          // TODO Auto-generated method stub 
          super.onPause(); 
          sonic.release(); 
          finish(); 
         } 
         @Override 
         public void onClick(View v) { 
          // TODO Auto-generated method stub 

         } 
         } 

Answer 1

dbHelp dbh = new dbHelp(this);把這個線OnCreate。